Filtration cartridges are well known and are used in the filtration of particulate, ionic, microbial and other contaminants from fluids in pharmaceutical, microelectronics, chemical and food industries. Filtration cartridges typically include a filtration material that has a plurality of longitudinal pleats arranged in a cylindrical configuration, a perforated cage disposed about the outer periphery of the filter element to permit fluid entry into the cartridge, and a perforated core coaxially disposed within the filter material. End caps are positioned at the ends of the filter material to prevent the egress of fluid from the cartridge. The ends of the filtration material are typically sealed by potting the ends of the filtration medium in an end cap, the end cap being in the form of a resin, a molten thermoplastic, or the like during a potting step.
Many filtration devices are constructed entirely of fluoropolymer materials to meet chemical and temperature resistance requirements, such as for use in the fabrication of semiconductors. The filtration material is pleated, and may include upstream and downstream drainage layers that are constructed of fluoropolymeric fiber materials (e.g., polytetrafluoroethylene (PTFE), perfluoroalkoxy alkane (PFA), fluorinated ethylene propylene (FEP), and polyvinylidene fluoride (PVDF) in the form of woven materials, non-woven materials, or nets.
Conventional methods to produce a high integrity seal between the end cap and the porous fluoropolymer membrane incorporate a meltable thermoplastic strip, such as a strip of FEP or PFA, at the two peripheral edges of the filtration material. Typically, these thermoplastic strips are about 6 to 13 mm in width and are located between the porous membrane and the downstream and/or upstream support layer. Ends of the filtration devices are joined to an end cap via a hot melt process which embeds the porous membrane edges in an adhesive bond to the end cap by thermoplastic bonding with the thermoplastic strip.
In some high purity filtration applications, such as applications that may be sensitive to contamination from extraneous materials, it may be undesirable to use strips of thermoplastic or imbibe a portion of the filtration medium with a thermoplastic material. In addition, in conventional devices, the filtration material protrudes from the filtration device the same or approximately the same distance. If dissimilar materials are used for the upstream and downstream drainage layers, when heated, the one of the drainage layers and the porous membrane layer may retract away from the cut interface into the device, thereby leaving only the other drainage layer at the embed interface between the end cap and filtration material. In such a situation, the porous membrane does not contact the end cap components, which results in an inadequate seal between the end cap and the filtration material.
Thus, there exists a need in the art for a filtration material that forms a high integrity seal between the porous membrane and the end caps without the use of a thermoplastic strip or an imbibed thermoplastic material.